Polymorphism in poly(vinylidene fluoride) nanoparticles prepared by a precipitation method: roles of the stirring rate, temperature and molecular weight

Abstract

Nanoparticles of poly(vinylidene fluoride) (PVDF) have been prepared by a precipitation method. The influence of preparation conditions, such as the stirring rate, temperature and molecular weight, on the morphology and crystalline structures, especially the polymorphic behavior, has been studied in detail. It is found that the average size of PVDF nanoparticles is mainly affected by the medium temperature and molecular weight, while the size distribution is influenced by all these factors. The crystallinity is less affected by the molecular weight but increases evidently with increasing temperature and stirring rate. The influence of these factors on the polymorphic behavior is complicated. First, a simultaneous increase in both β and γ phases has been achieved by increasing the stirring rate. Second, the β-PVDF crystals increase remarkably, whereas the γ-PVDF crystals decrease slightly with decreasing temperature, resulting in an obvious increase in the electroactive phases. Moreover, the increase in the PVDF molecular weight negatively affects the β-phase formation but positively affects the γ-phase formation, leading to an almost constant content of the electroactive phases. Ultimately, PVDF nanoparticles with the highest β-phase content of 74.6% and an overall electroactive phase content of 88.1% are prepared with 180 kDa PVDF under 2000 rpm and at 0 °C.